This application is based on and claims priority under 35 U.S.C. xc2xa7 119 with respect to Japanese Patent Application Nos. 2000-161277 and 2001-121648, the entire content of which is incorporated herein by reference.
The present invention generally relates to pulse generating circuit for motor rotations. More particularly, the present invention pertains to a pulse generating circuit for motor rotation generating pulse in accordance with the rotation number of a direct current motor having brushes. The pulse generating circuit for motor rotation of the present invention is applied as a detecting means for detecting the position of a movable member for performing the positional control or avoiding a dangerous contact with the movable member of the movable members such as seats for vehicles, window regulators, and sunroofs.
U.S. Pat. No. 5,497,326 and U.S. Pat. No. 4,463,426 disclose pulse generating circuit for motor rotations of this kind applied to the position adjusting controller for vehicle seat.
The pulse generating circuit for motor rotations applied to the position adjusting controller for vehicle seat in the aforementioned publications include a pulse forming means for forming ripple component included in drive electric current driving a direct current motor (hereinafter called motor) into a pulse mode and thus for outputting the ripple pulse. The ripple pulse outputted from the pulse forming means is counted following a control program of a microcomputer. Based on the counted value, the position of the seat moved by the motor rotation is calculated by the microcomputer. The micro computer memorizes the calculated seat position. The motor rotation is controlled to automatically move the seat to the memorized position by the switching operation by occupants.
The microcomputer of the positional adjusting controller for vehicle seat disclosed in U.S. Pat. No. 5,497,326 structures a control program for comparing current interval of the ripple pulse (hereinafter called pulse interval) and average interval of previous ripple pulses (hereinafter called average pulse interval) and for performing the ripple pulse correction when the pulse interval is greater than 150% of the average pulse interval. According to the ripple pulse correction based on the control program, when the ripple pulse is not outputted when expected (hereinafter called pulse error), skipped ripple pulse is supplemented by superimposing a pulse to correct the pulse error.
Thus, the ripple pulse accurately compliant with the rotation number of the motor can be obtained to enable to calculate the position of the seat accurately by the microcomputer.
The pulse interval of the ripple pulse becomes greater than 150% of the average pulse interval when the pulse error occurs due to change with time of the motor (i.e., wear of the sliding surface between brushes and commutators, which are components of the motor, by the motor rotation). However, the pulse interval of the ripple pulse also becomes greater than 150% of the average pulse interval when the pulse error does not occur, due to a sudden change of the rotational speed of the motor by the fluctuation such as sudden decrease of the drive voltage of the motor and load fluctuation such as lock of the motor.
According to the microcomputer of the positional adjusting controller for the vehicle seat shown in U.S. Pat. No. 5,497,326, the ripple pulse is corrected when the pulse interval of the ripple pulse is greater than 150% of the average pulse interval. As a result, the ripple pulse correction is performed by supplementing the pulse even when the pulse error is not generated and the ripple pulse correction is not necessary. Accordingly, the ripple pulse which has been compliant with the rotation number of the motor becomes inaccurately compliant with the rotation number of the motor, and thus the seat position cannot he accurately detected.
In light of the foregoing, a need exists for a motor rotation pulse generating circuit which addresses at least the foregoing drawbacks associated with always obtaining accurate ripple pulse in compliance with the rotation number of the motor.
In light of the foregoing, the present invention provides a pulse generating circuit for driving DC motor which includes a ripple pulse forming circuit for forming and outputting a ripple pulse from a ripple component in an electric current for driving the DC motor, a first signal generating means for outputting a first signal corresponding to a rotational number of the DC motor based on the electric current or voltage for driving the DC motor, a judging circuit for calculating a frequency ratio between the ripple pulse and the first signal and judging whether the deviation of the ratio is greater than a predetermined value compared to a predetermined fixed value, and a correcting circuit for correcting the outputted ripple pulse when the deviation of the frequency ratio is judged to be greater than the predetermined value and maintaining the outputted ripple pulse when the deviation of the ratio is judged to be equal to or less than the predetermined value.
According to the technical means mentioned above, ratio between the ripple pulse outputted from the pulse forming circuit and the signal output from the signal generating means is not changed even when the pulse interval of the ripple pulse becomes longer than the average pulse interval by the sudden change of rotational speed of the direct current motor. Accordingly, when the correction of the ripple pulse is performed by the correcting means, the sudden change of rotational speed of the direct current motor will not affect the performance and thus, the correction of the ripple pulse is performed only when the pulse error occurs. In consequence, the accurate ripple pulse complying with the rotation number of the motor can be always obtained. Since judging, correcting, and pulse forming are performed by circuits and do not depend on the control program, it is not necessary to consider load calculation, and thus the accuracy of the ripple pulse correction can be improved.
Preferably, the pulse generating circuit for driving DC motor of the present invention further includes a clock signal generating circuit for generating a clock signal based on the ripple pulse and the first signal and a filtering circuit disposed between the DC motor and the ripple pulse forming circuit for variably filtering a cut-off frequency of the ripple pulse based on the clock signal. The first signal outputting circuit inputs the first signal to the judging circuit as the clock signal.
According to the aforementioned technical means, the cut-off frequency of the filtering circuit is varied based on the clock signal generated based on the ripple pulse and the signal outputted from the signal generating means. Accordingly, the cut-off frequency of the filtering circuit can be following the change of the rotational speed of the direct current motor, the noise of the direct current motor is removed, and the ripple pulse which accurately complies with the rotation number of the direct current motor can be generated. Since the signal from the signal generating means is outputted to the judging circuit as the clock signal, the circuit structure can be simplified.
Preferably, the judging circuit includes a first counter circuit for counting the number of pulse of the first signal and resetting the counted value by the input of the ripple pulse and for outputting a correction signal correcting the ripple pulse to the correcting circuit when the counted value exceeds a first predetermined value during the time until the resetting of the counted value.
Preferably, the pulse generating circuit for dividing DC motor includes a masking circuit disposed between the first counter circuit and the correcting circuit for masking the output of the correction signal from the first counter circuit to the correcting circuit when the ripple pulse is inputted and such inputted ripple pulse is irregular.
According to the aforementioned technical means, unstable ripple pulse at start of the direct current motor can be removed to perform accurate ripple pulse correction.
Preferably, the pulse generating circuit for driving DC motor further includes a second counter circuit for counting the number of pulse of correction signal and a defect detecting circuit for outputting a signal indicating a circuit defect when the value of the counted value of the second counter circuit exceeds a second predetermined value.
According to the foregoing technical means, the circuit defect that occurs when the feedback does not function normally by the clock signal generating means can be easily detected from the outside based on the detect indicating signal outputted from the defect detecting circuit.